unconditionally use ThemeContext in EmotionElement

.changeset/light-swans-guess.md

@@ -0,0 +1,6 @@
+---
+'@emotion/react': patch
+---
+
+
+Use theme context when rendering components at all times. This removes a conditional usage of a React hook that could break [Rules of Hooks](https://reactjs.org/docs/hooks-rules.html) in some scenarios.

packages/react/__tests__/element.js

@@ -0,0 +1,46 @@
+// @flow
+/** @jsx jsx */
+import 'test-utils/dev-mode'
+import { render } from 'react-dom'
+import { jsx, css, CacheProvider, ThemeProvider } from '@emotion/react'
+import createCache from '@emotion/cache'
+
+// $FlowFixMe
+console.error = jest.fn()
+
+beforeEach(() => {
+  // $FlowFixMe
+  document.head.innerHTML = ''
+  // $FlowFixMe
+  document.body.innerHTML = `<div id="root"></div>`
+
+  jest.clearAllMocks()
+})
+
+describe('EmotionElement', () => {
+  test('no React hook order violations', () => {
+    const theme = { color: 'blue' }
+    const cache = createCache({ key: 'context' })
+
+    // $FlowFixMe
+    const Comp = ({ flag }) => (
+      <ThemeProvider theme={theme}>
+        <CacheProvider value={cache}>
+          <div
+            css={
+              flag &&
+              (t => css`
+                color: ${t.color};
+              `)
+            }
+          />
+        </CacheProvider>
+      </ThemeProvider>
+    )
+
+    render(<Comp />, document.getElementById('root'))
+    expect(console.error).not.toHaveBeenCalled()
+    render(<Comp flag />, document.getElementById('root'))
+    expect(console.error).not.toHaveBeenCalled()
+  })
+})

packages/react/__tests__/global.js

@@ -2,14 +2,25 @@
 import 'test-utils/dev-mode'
 import * as React from 'react'
 import { render, unmountComponentAtNode } from 'react-dom'
-import { Global, keyframes, css, CacheProvider } from '@emotion/react'
+import {
+  Global,
+  keyframes,
+  css,
+  CacheProvider,
+  ThemeProvider
+} from '@emotion/react'
 import createCache from '@emotion/cache'
 
+// $FlowFixMe
+console.error = jest.fn()
+
 beforeEach(() => {
   // $FlowFixMe
   document.head.innerHTML = ''
   // $FlowFixMe
   document.body.innerHTML = `<div id="root"></div>`
+
+  jest.resetAllMocks()
 })
 
 test('basic', () => {
@@ -67,3 +78,29 @@ test('updating more than 1 global rule', () => {
   renderComponent({ background: 'gray', color: 'white' })
   expect(document.head).toMatchSnapshot()
 })
+
+test('no React hook order violations', () => {
+  const theme = { color: 'blue' }
+  const cache = createCache({ key: 'context' })
+
+  // $FlowFixMe
+  const Comp = ({ flag }) => (
+    <ThemeProvider theme={theme}>
+      <CacheProvider value={cache}>
+        <Global
+          styles={
+            flag &&
+            (t => css`
+              color: ${t.color};
+            `)
+          }
+        />
+      </CacheProvider>
+    </ThemeProvider>
+  )
+
+  render(<Comp />, document.getElementById('root'))
+  expect(console.error).not.toHaveBeenCalled()
+  render(<Comp flag />, document.getElementById('root'))
+  expect(console.error).not.toHaveBeenCalled()
+})

packages/react/src/emotion-element.js

@@ -88,9 +88,7 @@ let Emotion = /* #__PURE__ */ withEmotionCache<any, any>(
     let serialized = serializeStyles(
       registeredStyles,
       undefined,
-      typeof cssProp === 'function' || Array.isArray(cssProp)
-        ? React.useContext(ThemeContext)
-        : undefined
+      React.useContext(ThemeContext)
     )
 
     if (

packages/react/src/global.js

@@ -40,9 +40,7 @@ export let Global: React.AbstractComponent<GlobalProps> =
     let serialized = serializeStyles(
       [styles],
       undefined,
-      typeof styles === 'function' || Array.isArray(styles)
-        ? React.useContext(ThemeContext)
-        : undefined
+      React.useContext(ThemeContext)
     )
 
     if (!isBrowser) {